1. Field of the Invention
This invention relates to a piston for an axial piston machine, including a body forming an axial cavity, and a piece of filler material inserted into that cavity.
2. Description of the Prior Art
Such a piston, generally known as a slipper piston, is described and illustrated in DE-OS 19 20 140. In this known arrangement the core or filler body is screwed into the cavity in the piston. The inner and outer threads for this are at the inner end of the cavity or of the filler piece. A shoulder in the hollow body which engages in front of the outer end of the filler piece serves to axially secure the filler piece in the cavity. This shoulder is formed by a lock ring inserted in a groove in the wall of the cavity, and arranged between this lock ring and the outer end of the filler piece is a spring washer which urges the filler piece towards the bottom of the cavity. By this means the filler piece is axially secured on the one hand by the bottom of the cavity and on the other hand by the shoulder. It should be noted that the engagement of the thread cannot ensure axial securing of this kind because, owing to the play in the thread, the abrupt pressure and centrifugal force loading when the piston is in operation would deform the screw thread and considerably increase the play in the screw thread, which would necessarily lead to loosening of the filler piece.
In the above-mentioned known arrangement the axial securing is thus determined by the strength of the spring washer. If, when the piston is in operation, the forces acting on the filler piece and directed against the spring tension exceed the spring tension, rattleproof fastening of the filler piece in the piston is no longer guaranteed. It must also be taken into consideration that in the known arrangement the lock ring can wear its seat out or it could also be split. It is thus clear that in the known arrangement the axial securing is relatively insecure. In addition it has many component parts through which the manufacturing costs of the piston are increased.